Physical vapor deposition (PVD) is commonly used within the semiconductor industry, as well as within solar, glass coating, and other industries. A PVD system is to deposit metal layers onto substrates such as semiconductor wafers that is positioned in a vacuum plasma chamber. A PVD process is used to deposit a target material such as titanium or titanium nitride onto the semiconductor wafer. In a typical PVD system, the target materials to be coated are disposed in a vacuum chamber containing an inert gas such as argon. The metal layers can be used as diffusion barriers, adhesion or seed layers, primary conductors, antireflection coatings, etch stops, etc.
Theoretically, the target should be very wide relative to the semiconductor wafers so that the target represents an infinite source plane to the particle-receiving face of the semiconductor wafers. Unfortunately, the target has a finite size that is usually the same order of magnitude as that of the semiconductor wafers. Expelled or sputtered target atoms tend to leave the target in all directions, then collide with each other and scatter, arriving at the semiconductor wafers from a variety of angles. As a result, the metal layer in the areas of the etchings in the semiconductor wafer is formed unevenly, leaving a relatively thick lateral layer on the sidewalls of the etchings and a thin layer at the bottom of the etchings.